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INVENTOR. fd'warcic Creuiz BY; flaMflfiW 'lwi 2,916,17i REACTORACOMPVONENT Edward C. Creutz, Pittsburgh, Pa, assignor to the UnitedStates of America as represented by the United States Atomic EnergyCommission. v

Original appIicationMayZZ, 1945,-'S erial No. 595,182. Divided and thisapplication September 17, 1951, Serial No. 246,945 I 5 Claims. (Cl;206-84) This invention relates to neutronic reactors and to 'a novelarticle of manufacture used in and in combination with such reactors.This patent is a division of application Serial No. 595,182, filed May22, 1945.

In neutronic reactors, a neutron fissionable isotope such as U U or 94or a mixture thereof is subjected to fission by absorption of neutronsanda self-sustaining chain reaction is established-by theneutronsevolved by the fission. In general such reactors comprise bodies ofcompositions containing such fissionable material, for example, asnatural uranium, disposed in-a neutron slowing material which slow theneutrons to thermal energies. Such a slowing material is termed aneutron moderator. Carbon, beryllium, and D are typical'moderatorssuitable for such use. Heat is evolved during the reaction which isremoved by passage of a coolant through the reactor or in' heat exchangerelationship therewith. Specific details of the theory and essentialcharacteristics of such reactors are set forth in copending applicationof Enrico Fermi'and Leo Szilard, Serial No. 568,904, filed December 19,1944, now Patent Number 2,708,656.

In the operation of neutronic reactors at a substantial power, forexample, 1000 kilowatts or more, for more than a few minutes diificultycan be encountered due to the fact thatthe moderator and /or coolant canbecome highly radioactive due to the projection of fission fragmentsand/or recoils into the surrounding material during the operation of thereactor if the fissionable material is bare. This result canseriously... complicate operation of the reactor since the radioactivityof the coolant and moderator may constitute a serious hazard topersonnel if not completely shielded.

Improved neutronic reactors have been produced wherein the tendency ofthe moderator and/or coolant to become radioactive is substantiallyminimized. It has been found that this result may be secured byinterposing a solid non-fissioning barrier between the fissioningisotope and the coolant or moderator or both. Notwithstanding the factthat introduction of non-fissioning isotopes into a neutronic reactorabsorbs neutrons and,

therefore, may tend to prevent establishment of a neutron chainreaction, it has been discovered that it is possible to insertnon-fissioning barriers into the reactor, and to so proportion thethickness of the barrier to prevent passage :of all or a preponderantamount of fission fragments and/ or recoils from the fissioning isotopeinto the moderator and/ or coolant while yet avoiding use of such aquantity of barrier that the neutron absorption thereof preventsestablishment or maintenance of the neutron chain reaction. The barrieritself should be constructed of a material or materials having a lowneutron capture cross-section.

In accordance with the present invention it has been found that steelparticularly stainless steel which contains corrosion resistant elementssuch as nickel, chrominm and/ or cobalt, while having a comparativelyhigh neutron capture cross-section may be used as a barrier or sheathfor fissionable bodies in a reactor and has the advantage ofwithstanding high operating temperatures contact with fissioningcomposition.

when the barrierisin contact with a coolant.

In order to promote heat transfer from the fissioning isotope throughthe barrier to the contacting moderator and/or coolant, the barriershould be in close intimate Generally, special precautions are observedfor this purpose. Thus, a shell forming the non-fissioning barrier orsheath may be drawn or shrunk upon the fissioning component'whichpreferably is inthe metallic state. Therefore, the barrier mate-, rialmust be capable of bein'gshrunk or drawn to a very substantial degree sothat considerable reduction in the 7 diameter of the sheath or barriermay be effected after I the sheath has been fitted upon the fissionablebody. It

is possible to reduce stainless steel by at least 30 percent and thusobtain a very tight fit on the uranium or other fissionable material.These enclosed-fissionable components are used as the active componentof a neutronic reactor, and frequently are located in contact with acoolant, such as a gas or liquid coolant, for removal of heat from theenclosed fissionable components and from the reactor. Where the coolanthas a corrosive'effect upon the fissionable metal or other material, thenon: fissioning sheath also serves to protect the fissionable material.In such a case, every precaution, including choice of barrier material,must be takento prevent the order to seal the material from the coolant.The problem of welding or otherwise sealing the sheath or barrier aboutthe fissionable material, presents difliculties which are readilyovercome by the use of stainless steel as. the

sheathing material.

As previously noted, lengths of the fissionable bodies generally aredisposed in channels extending through or 1 at least into the moderator.Duringthe chain reaction the central interior portion of these bodiesfrequently rises to a temperature much above the temperature of the bodyexteriorwhich is in close'relationship with the coolant. f The barriermaterial must, therefore, be'capable of withstanding the temperature ofcontact with the fissionable component without deteriorating.

The provision of a new article composing a fissionable component and anenclosure or barrier therefor which is capable of surmounting theforegoing difiiculties and problems constitutes the principal objectsand advantages of the invention, others of which will become apparentfrom the following description and drawings in which:

Fig. l is a longitudinal sectional view of a fissionable body looselyenclosed in a barrier or sheath of steel;

Figure 2 illustrates the assembly of the steel jacket or barrier as itis drawn through a die into tight contact with the fissionable body; and

Figure 3 is a longitudinal view of the completely sealed, jacketed body.

As illustrated in the drawings, the invention generally comprises aprotective coating or jacket 2 of stainless steel completely enclosingand sealing a uranium rod 1.

Inasmuch as the stainless steel protective coating or jacket has theproperty of absorbing neutrons to some extent, it is desirable tomaintain the quantity of the steel within the pile at a minimum, inorder to make possible a chain reaction therein as previously discussed.Consequently, the thickness of the steel tubes and jackets. should bemaintained at the minimum required from the standpoint of strength,possible corrosion and erosion, and ability to restrain fission productsto a substantial; degree. Where the jacketed bodies are exposed directlyto the attack of a corrosive coolant, such as water, the:

Patented Oct. 27, 1959 Stainless steel is suitable for eliminating suchthey generally are made in relatively short lengths, for

instance, about 8 inches in length. Several methods may be employed forhermetically sealing the uranium body 1 in the thin jacket 2 ofstainless steel or similar material.

A disc 6 of stainless steel serves as a closure, and is tightly weldedto the open end of the jacket. If desired, disc 6 may be provided witharimor other projection 8 projecting outwardly from'the outer surface ofthe disc, and concentrically contiguous to the open end of the jacket 2.Sealing closed the 'open end of the jacket 2 is accomplished by weldingtogether the jacket 2 and the cap rim 8 as at 9. I

The assemblage may be constructed in the following manner. The uraniumrod 1 of proper dimensions is shot blasted, cleaned and polished.Thereafter, the rod 1 and cap 6 are introduced into the can or jacket 2,and the can is placed in a tightly fitting steel sleeve or die 3.Thereupon, the jacketed uranium rod and cap are forced by hydraulicpressure exerted upon piston 10 through the die usually at an elevatedtemperature. A second pass through a more restricting die may bedesirable to insure tight contact of the jacket with the rod. Theassemblage is then chilled; the edges of the cap rim 8 and the jacketare welded together; and the extending edges turned inwardly intocontact with the end cap 6. A second or outer stainless steel cap 12 isthereafter welded to the jacket 2 exterior of the inner cap or disc 6.

The jacketed bodies after production may be disposed in the channelsof aneutronic reactor in end to end relationship. The usual structure of acarbon moderated reactor comprises a carbon cube with horizontalchannels in which the jacketed fissionable bodies lie and through whichthe coolant passes. The jacketed bodies herein described may be usedefiectively in this or other type of reactor. Fissionable bodies otherthan natural uranium such as U U mixtures containing more than naturalconcentrations of U or other Th or U mixtures with fissionable isotopessuch as U U or 94 may be providedwith a sheath as herein contemplated.

It will be apparent to those skilled in the art that variousmodifications may be made without departing from the principles of theinvention as disclosed herein, and for that reason, it is not intendedthat the invention should be limited other than by the scope of theappended claims.

What is claimed is:

1. An article of manufacture comprising, a cylindrical container havingat least one open end, a cylindrical solid body snugly disposed withinthe container,- the wall of the container being bent around the body atthe open end of the container leaving an aperture, an inner cap and anouter cap, the inner cap being disposed between the solid fibody and theopen end of the container and having peripheral edges extendingtherefrom conforming to the wall of the container, the inner capbeingsealed to the bent portion of the container, and the outer cap beingstructed of stainless steel.

3. An article of manufacture comprising the elements of claim 2 whereinthe solid body-contains a material fissionable by neutrcnsof thermalenergy.

4. An article of manufacture oomprising, in combination, a solid body, acontainer disposed about'said body having at least one open end, aninner cap, and. an; outer cap, the. inner cap being disposed between theouter cap and the solid body and being provided with an extension at theextremity thereof. conforming to the inner surface of the container, theportion of the container adjacent to the open end and the adjacentportion of the; extension being bent inwardly around the end of thesolid body and sealed together, and the outer cap being sealed to theexposed surfaces of the container adjacent to the aperture.

5. An article of manufacture comprising the elements of; claim 4 whereinthe container and outer cap areconstructed of stainless steel.

, References Cited in the file of this patent UNITED STATES PATENTS

